I use OneBag3 and while normally installed it uses the round edged square container without the grey eagle or falcon that you would normally see with the default UI. If you go look into the Blizzard Interface Art files under ContainerFrame all of the blps there are for 1Slot, 1x4, 1x4+2, 2x4, 3x4, etc and have a lot more than just a normal container, 1 button with a border.

My question is is there any way I could change the border of the container frames, which hold the items in your backpack/bags, without having to somehow edit all of these blps as there are 25 files that would need to be edited.

All I want to do is change the round edged container that hold your items in your bags to a more squared look.